Electrostatic printing apparatus having improved counter-electrode

ABSTRACT

Electrostatic printing apparatus for printing on bottles in which the means forming a counter-electrode within the bottle includes means forming circular upper and lower corona discharge gaps centered on the bottle axis comprising axially spaced electrode terminals and a circular electrode coaxial with the bottle axis and between the terminals.

United States Patent [191 Fisher et al.

[ July 23, 1974 [73] Assignee: Purex Corporation, Ltd., Lakewood,

Calif.

22 Filed: Aug.1l,1970 [21] Appl.No.:62,983

[56] References Cited UNITED STATES PATENTS 3,359,890 12/1967 Fredrickson 101/D1G. 13 3,413,917 12/1968 Fisher et a1. 101/114 3,421,050 1/1969 Topper et a1. 1 .1 317/3 3,518,488 6/1970 Michalchik 317/3 Primary Examiner-Robert E. Pulfrey Assistant Examiner-E. l-l. Eickholt [5 7] ABSTRACT Electrostatic printing apparatus for printing on bottles in which the means forming a counter-electrode within the bottle includes means forming circular [52] US. Cl 101/114, l0'l/DIG. 13, 317/3, upper and lower corona discharge gaps centered on 1 313/326 the bottle axis comprising axially spaced electrode ter- [51] InLCl B411 15/00 minals and a circular electrode coaxial with the m [58] Field of Search IOl/DIG. 13, 1:14; 317/3; axis and between the terminals v a 313/326 9 Claims, 4 Drawing Figures 1 80 i TO .DC.

Ac. VOLTAGE nc. VOLTAGE ELECTROSTATIC PRINTING APPARATUS T HAVING IMPROVED COUNTER-ELECTRODE I 3 BACKGROUND OF THE INVENTION 1. Field of the Invention.

This invention has to do with electrostatic printing or for like purposes depositing printing particles onto objects, particularly bottles such as plastic bottles.

As disclosed in US. Pat. No. 3,521,558 issued July 21, 1970, (Ser. No. 767,018, filed Aug. 26 1968) which is hereby incorporated by charged particles may be deposited through a stencil Onto an object by launching the particles by a launching electrode spaced behind the stencil and toward the object where a counter-electrode condition is maintained to attract the particles onto the object surface in the pattern determined by the stencil aperturing.

2. Prior Art. 7

In our US. Pat. No. 3,413,917, also incorporated by reference herein, a form of counter-electrode is describedfin which pointed electrode terminals are directed horizontally at the back of a bottle surface to be printed, projecting outwardly from a circular electrode surrounding the pointed electrodes rearwardly of the electrode tip. As described, this configuration of counter-electrodewas designed to provide ionized air within the bottle behind the printing area, thus to provide an attraction for launched, oppositely charged particles.

In practice, however, andwith larger print areas, it was found-that a discernible deviation from print uniformity unfortunately was encountered apparently traceable to a disuniform the container. I

SUMMARY or THE ENTION It isa majorobjective, accordingly, of the present invention; to provide, novel counter-electrode means capable of providing uniform gas ionization conditions behindthe print area and thus to improve uniformity of printing particle deposit in printing.

In general, this objective is realized by providing corona discharge centered on the bottle axis. Specifically, the invention. provides in an electrostatic'pr inting apparatus'for printing on a bottle surface including a printing particle supply, a stencil spaced from the. bottle surface and an electrode spaced beyond the stencil and adapted to launch the particles through the stencil to print on a preselected printing area of the bottle surface opposite the stencil, the improvement comprising'electrode structure within the bottle forming upper and lower corona discharge gaps circular in horizontal cross-section and centered on the bottle axis to form a uniform counter-electrode condition within the bottle. The electrode structure typically includes spaced axially aligned electrode terminals and a circular electrode between the electrode terminals and co axial-therewith, the circular electrode typically extends circumferentially of the bottle axis behind the printing area. The spaced electrodes comprise a pair of oppositely directed, pointed electrodeterminals aligned on the bottle axis and respectively spaced above and below the circular electrode to define therewith the circular upper and lower corona discharge gaps. In certain preferred embodiments there is provided an elongated conductive needle extending coaxially within the bottle havingtermination's defining the spaced electrode terreference, electrically gas ionization pattern within BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a schematic view of the present apparatus;

FIG. 2 is a view in vertical section of a bottle and counter-electrode arranged according to the invention;

FIG. 3 is an illustration of printing achieved with a uniform counter-electrode condition within the bottle; and

FIG. 4 is an illustration of varying print density encountered with other than a uniform countepelectrode condition within the bottle.

. Referring now to the drawings in detail there is shown in FIG..1, an apparatus according to the present invention, particularly adapted to print or decorate an openmouth container 10 having a printable surface 10a whichmay be dielectric, e. g., of glass'or of syntheticorganic plastic material such as polyethylene or polyvinyl chloride or paper or a plastic/metalor paper/metal combination. Printing means for depositing electrically charged particles upon the container surface are shown including a printing'particle supply comprising a hopper 12 having within a charging wire 14 connected to, e.g. a positive DC source (not shown) forcharging printing particles 16, a conveyor belt 18, suitably of rubber or mohair, and driven continuously beneath the hopper outlet between sheaves'20. Printing particles 16, electrically charged within the hopper, fallby gravity onto the belt 18 and are carried area. There launching electrode 22 nected at 24 to, illustratively, the positive terminal 26 of a DC voltage supply 28 so that the particles 16 are repelled by the electrode 22 and thus launched as a stream 30. A brush 32 rotating about electrode 22 may be used, to assist in separating charged particles from the belt.

A counter-electrode means generally indicated at 34 within container 10 is provided to define an electrostatic field with launching electrode 22. The counterelectrode means 34 to be later described in detail is connected at 36 through switch 38d and line 39 to, illustratively, the negativeterminal 40 of the DC voltage supply 28 so that the particles of stream 30 are attracted to the counter-electrode 34 and surface 10a. Within the field thus defined there is placed a printing to the launching 'pattem defining stencil 42 of conductive or dielectric is provided conunmasked areas of the sheet, or by other suitable means. I

It will be appreciated that the foregoing specific arrangement and function of components can be varied and use still be made of the present invention. Thus, for example, the stencil can function as the launching electrode as well as a pattern determinator or the stencil can be placed against the container surface. In general, any printing system in which printing particles are moved through an electrical field to be placed on a surface in a stencil controlled pattern can be improved in resultant print appearance by the present invention.

In the above described apparatus as best shown in FIG. 2, a particular form of counter electrode 34 is provided to form circular upper and lower corona discharge gaps at Hand 54 respectively each centered on the bottle axis 62. The counter electrode 34 is seen to include a conductive needle 56 having opposed terminations forming axially spaced, pointed and oppositely directed electrode terminals namely upper terminal 58 and lower terminal 60 which are aligned on the bottle axis 62 and a circular electrode 64 to define the discharge gaps 52, 54. The needle 56 is connected by line 66 extending through sleeve 68 to a voltage supply 70. The circular electrode 64 is connected by line 72 through sleeve 74'and resistor 76 to ground. A dielectric'or nonconductive body 78 generally cylindrical in horizontal cross-section and formed, e.g., of Lucite (polymethylmethacrylate) and supported by means not shown, is provided surrounding the needle 56 in a manner to expose the opposite ends thereof forming the electrode terminals 58, 60 of the counter-electrode 34. The needle 56 is mounted within and axially of the body 78 and is supported thereby along the bottle axis 62. The circular electrode 64 which may take the form of a circular cross section ring or torus, as shown in FIGS. land 2, or which may be a fiat surfaced band, is mounted on the body 78 by suitable means not shown and preferably equidistantly spaced between upper and lower, electrode terminals 58, 60. Particularly preferred is a symmetrical diamond pattern of electrodes in cross section as shown; Thus arranged, application of suitable potential to needle'56 locally concentrates charge atboth upper and lower electrode terminals 58, 60 and establishes a field with circular electrode 64. When the field dielectric strength around the terminals 58 and 60 is sufficient to cause a corona discharge through the air and air ionization, these terminals discharge to the circular electrode and ionize the air therebetween. The result is an upper and lower somewhat conical and somewhat toroidal but cross sectionally, circular, cascade of air ions radially of the electrode terminals 58, 60 and toward the circular electrode 64 in the gaps 52, 54. This upward and downward fountain of ions forms a virtual cylinder of ions within the bottle and'thus a highly uniform counter-electrode condition within the bottle, whereby particle deposition is more uniform across the bottle surface 10a and printing density is consistent across all lettering or other indicia.- See FIG. 3. In FIG. 4, the result of locally high ionization is depicted, such as might be encountered with electrode terminals directed toward the back of the container surface to be printed.

of a voltage differential to the electrodes in a known manner and typically by application of 40,000 to 60,000 volts to the launching electrode and 10,000 to 20,000 volts of opposite polarity to the needle 56 of the counter-electrode 34.

The stencil is generally grounded 0r unconnected as shown in FIG. 1, but may be given a potential level intermediate the electrode voltage values, e. g., by closing switch 48.

Following printing a reversing charge may be applied through electrode assembly 34 to reduce the charge on the container interior surface 10b, but at less voltage than would relaunch the particles deposited on the outside of the container. A reduction of interior charges to neutrality is not required, only reversal toward neutrality but neutralization may be carried out. For this purpose an AC voltage source 80 may be provided to which the counter electrode 34 is connectible through line 86 and switch position 38a. With reference to FIG. 1, closing switch 38 to the left, from position b to position a, and closing switch 82 introduces interiorly of container 10 an AC voltage, e.g. at 1,000 to 20,000 volts. For the conditions of printing given above a 5,000 volt AC charge to the container interior for from I to 10 seconds, preferably 3 to 7 seconds reverses the interior charge condition sufficiently toward neutrality to alleviate particle migration and enable retention of image area integrity. While an AC voltage application is illustrated, an opposite polarity DC charge, including a pulsing DC voltage, may be used with effectiveness, at levels below those relaunching the deposited particles, in which case switch 38 is placed at position c, switch 82 is opened and a positive voltage from terminal 26 is applied to needle electrode 56 through line 88, while circular electrode 64 is grounded through resistor 84.

In the illustrated embodiments herein, the counterelectrode and reversing electrodes are shown to be one and the same. This has proved to be a practical expedient in practice as well as being convenient in illustrating the invention. Switch 38 is capable of four positions: extreme right position d, for connection of the counter-electrode needle 56, 34 to negative DC; extreme left position a, for connection thereof to AC; middle left position b, for no connection and middle right position c, for connection to positive DC.

A further assist in rapid reduction-of potential is realized by creating a reversing charge attracting condition exteriorly of the container. Thus, application of a negative charge reversing positive voltage within the container is heightened in charge neutralizing effectiveness by creating a charge condition which attracts the neutralizing positive charges to the negatively charged area. Conveniently in stencil printing, advantage may be taken of the proximity of the stencil to the image area, to apply a charge to the stencil which attracts the reversing charge applied within the container. For instance, assuming a launching electrode at +50,000 volts and a negative counter-electrode at "15,000 volts, and application following printing of 5,000 volts AC to the counter-electrode needle 56 for about 5 seconds, more complete dissipation of the image areanonimage area potential is realized if during the AC application there exists a negative charge on the stencil 42. This negative charge should be on the stencil 42 during internal charge reduction within the container 10. It is not necessary that the opposite polarity charge r be applied to the stencil simultaneously with application of a charge reversing voltage to the container interior, for the opposing charge on the stencil will remain following its application to the stencil sufficiently to realize the benefits discussed above.

- For illustrative purposes herein, the launcher has been considered to be positively charged and the probe therefore negatively charged during printing. The particles were then positively charged. It is to be noted that it is the relationship of polarities of the electrodes to one another and to the particles and their absolute a printing particle supply, a stencil spaced from the bottle surface and an electrode spaced beyond the stencil and adapted to launch the particles through the stencil to print on a preselected'printing area of the bottle surface opposite the stencil, the improvement comprising electrode structure within the bottle forming plural adjacent coaxial corona discharge gaps circularly of the bottle axis to provide a counter-electrode condition rearwardly of said preselected printing surface and within the bottle.

2. Apparatus according to claim 1 in which said structure includes spaced axially aligned electrode terminalsanda circular electrode between the electrode terminals and coaxial therewith.

3. Apparatus according to claim 1 in which said structure includes a circular electrode extending circumaxially of the bottle-axis behind said printing area, a pair of oppositely directed, pointed electrode terminals aligned on the bottle axis and respectively spaced above and below the circular electrode to define therewith said circular upper and lower corona discharge p 4. Apparatus according to claim 3 including also means applying a voltage to said electrode terminals.

5. Apparatus according to claim 4 in which said voltage means includes an AC voltage supply and a DC voltage supply connectible alternatively to said electrode terminals.

6. Apparatus according to claim 1 in which said structure includes an elongated conductive needle ex-. tending coaxially within the bottle having terminations defining said spaced terminals, a nonconductive body surrounding all but said needle terminations and supporting the needle in said bottle, and a circular electrode also supported by the body and in circumferentially spaced relation to the needle equidistantly from 

1. In an electrostatic printing apparatus for printing on the surface of an axially extended bottle including a printing particle supply, a stencil spaced from the bottle surface and an electrode spaced beyond the stencil and adapted to launch the particles through the stencil to print on a preselected printing area of the bottle surface opposite the stencil, the improvement comprisiNg electrode structure within the bottle forming plural adjacent coaxial corona discharge gaps circularly of the bottle axis to provide a counter-electrode condition rearwardly of said preselected printing surface and within the bottle.
 2. Apparatus according to claim 1 in which said structure includes spaced axially aligned electrode terminals and a circular electrode between the electrode terminals and coaxial therewith.
 3. Apparatus according to claim 1 in which said structure includes a circular electrode extending circumaxially of the bottle axis behind said printing area, a pair of oppositely directed, pointed electrode terminals aligned on the bottle axis and respectively spaced above and below the circular electrode to define therewith said circular upper and lower corona discharge gaps.
 4. Apparatus according to claim 3 including also means applying a voltage to said electrode terminals.
 5. Apparatus according to claim 4 in which said voltage means includes an AC voltage supply and a DC voltage supply connectible alternatively to said electrode terminals.
 6. Apparatus according to claim 1 in which said structure includes an elongated conductive needle extending coaxially within the bottle having terminations defining said spaced terminals, a nonconductive body surrounding all but said needle terminations and supporting the needle in said bottle, and a circular electrode also supported by the body and in circumferentially spaced relation to the needle equidistantly from both terminals to define therewith said corona discharge gaps.
 7. Apparatus according to claim 6 including also means applying a voltage to said electrode terminals sufficient to cause an air ionizing corona discharge between said terminals and said electrode.
 8. Apparatus according to claim 7 in which said voltage means includes an AC voltage supply.
 9. Apparatus according to claim 8 in which said voltage means includes DC voltage supply. 